Fly fisherman typically want to have dozens of flies at their disposal for use in a fishing expedition, so that different types of flies can be tried for their success. The flies are kept in fly boxes, which are relatively small, flat, hinged boxes with a closure. Fly fisherman commonly carry from four to eight of these boxes, each of which can hold up to $500.00 worth of flies. The boxes often have a ridged insert piece into which the hooks can be buried. The piece is designed so that the bodies of the flies can sit within the grooves of the piece in order to protect them from damage.
Fly fisherman often must walk some distance to access a stream or lake. Any extra weight carried by fisherman is thus an important consideration. Fly boxes in use today are typically made from a metal or hard plastic case with a soft plastic insert for holding the flies. These boxes weigh from three to five ounces each. Accordingly, a full complement of boxes can weigh anywhere from one to five pounds, which is substantial considering the distance any fly fisherman must walk, and the amount of time fisherman spend standing with the boxes on their person.
Additional important considerations for fly box design are the opening and closing of the box, and whether the boxes can float. It is important that the boxes are relatively easy to open, especially in cold weather use, when dexterity is a problem. In addition, as the boxes can hold hundreds of dollars worth of flies, if one is dropped and quickly sinks, there could be a substantial monetary loss, not to mention the loss of the use of the flies for the balance of the fishing trip. Yet another consideration is the life of the hinge. The hard plastic polystyrene boxes are typically of a unitary design, in which the hinge is a so called "living" hinge which is molded directly into the box. Polystyrene tends to fatigue with time, however, and so the hinge eventually begins to tear, necessitating replacement of the box. A final consideration is that the hard exteriors of these boxes does not allow flies, or the needles used for clearing the eyes of hooks, to be held temporarily on the outside of the box, which is desirable for quick access to at least a small number of flies, or the needle, in order to save time and effort.